1. Field of the Invention
The invention relates to induction motor auxiliary external cooling systems, and more particularly to external auxiliary cooling systems for totally enclosed fan cooled (TEFC) induction motors that enhance external transfer away from the motor housing and cooling efficiency.
2. Description of the Prior Art
Known TEFC motors are sealed from ambient air, and are often used in harsh environments—weather related or potentially volatile atmospheres that are not suitable for exposure to live electrical power sources. Generally TEFC motors dissipate internal heat by conductive heat transfer through the motor housing. Housing heat transfer is often enhanced by addition of rows of cooling fins projecting from the housing and an external fan/fan shroud that directs cooling air over the external cooling fins. External fan-induced airflow over the fins enhances convective heat transfer away from the motor cooling fins to ambient atmosphere. It is challenging to provide sufficient external cooling air flow over TEFC motor cooling fins—especially when the motor is subjected to a heavy external driven load operating condition. Often a TEFC motor housing or yoke is constructed of cast iron or cast steel, with integrally cast cooling fins. Those metals have lower thermal conductivity than other metals, such as copper or aluminum. Copper or aluminum may not have sufficient structural strength for higher power induction motor housings. It is not always economically feasible to construct TEFC motor housings from steel or cast iron, and then attach higher conductivity copper or aluminum cooling fins to the housing exterior. An additional heat transfer challenge for TEFC motors is their use of exterior paint and/or sound-deadening coatings that are relatively poor thermal conductors. Those coatings further degrade heat transfer capabilities of TEFC motor housings.
Under extreme motor load conditions the only practical recourse may be to substitute a more expensive totally enclosed water cooled motor for a TEFC motor. While the substitution may be acceptable for new motor installations, it may not be practical or cost effective to swap out a TEFC motor for new water cooled motor if the shop floor does not have an available cooling water source. Some operating environments are not suitable for water cooled motors. Retrofitting a water cooled motor for an otherwise adequately functional TEFC motor is disruptive to shop activities, requires capital purchase and installation costs for the replacement motor, and costs associated with discarding the old motor. It is more desirable to retrofit existing TEFC motors with enhanced cooling capabilities rather than swap them out with totally enclosed water cooled motors. New enhanced cooled TEFC motors give motor users more flexibility in choosing motor types suitable for their applications.